my 2in female salvini has nice pointed fins and with other species this really doesnt stay true even 99% of the time so i would stay away from trying to sex by their fins unless you have a male right next to a female to compare and this is only part of the characteristics you are using to sex them. as for FM i think you have to just get a couple and grow them out and find one that way, this will be cooler anyways because it allows you to have more fish/activity in the tank when everything is little and if you get multiple males you can pick out the one with the best coloring/personality. and yeah like others have said femal salvinis will have black in their dorsal and nice big red blotch on their bellies and will be more brightly yellow, they will show these colors even when little, my little female salvini i just got is not even 2in yet and she is as colorful as the one in the first link you posted so just pic the one that has the most spangling and non-female specific coloration
